Tiny Electric Signals Could Predict Earthquakes or Bridge Failures

In the final seconds before a powdery material forms an avalanche or cracks, it emits an electrical signal. New studies of this strange effect could help scientists predict real-life avalanches and earthquakes.

In the early hours of January 17, 1995, fishermen were already hard at work in Japan's Osaka Bay when they noticed a strange orange light shoot across the distant shore. They watched as the luminous object, 100 meters tall, swept left-to-right across the ground until it crashed into a nearby mountain range. Then lightning struck from the sky. A few seconds later, the water beneath the boats began sloshing—a magnitude 6.8 earthquake had just struck.

What those fishermen were feeling was the Great Hanshin earthquake, and what they were seeing was "earthquake lights." These balls and columns of light that seem to co-occur with seismic activity have been recorded in thousands of anecdotes. They've been recorded scientifically too, but they still defy explanation.

Scientists from Rutgers University may have stumbled upon an answer. They discovered that clumps of fine particles emit electrical voltages just before they crack. A better understanding of this unexpected electrostatic property may one day help to predict earthquakes, avalanches, mine shaft collapses, and bridge failures.

Considering these potential applications, the discovery comes from an unexpected place. Physicist Troy Shinbrot normally studies the ways in which pharmaceutical powders stick together during the manufacturing process. But one day, inspired by historical reports of earthquake lights, Shinbrot decided on a whim to conduct a small experiment with some equipment around the lab. He and his students added a few scoops of finely ground Tylenol into a slowly spinning cylinder, but didn't expect to observe anything interesting.

Like laundry in a washing machine, the powder stuck to the sides of the spinning cylinder and built up there. But after reaching a certain height, the powder would crack and tumble back down to the bottom. (Imagine trying to build a mountain out of flour or some other powdery substance. When the sides get too steep, it comes crumbling down.)

Inside the tumbler, the mini avalanches created voltages higher than 100 volts. That wasn't altogether surprising. Solids such as glass, rock, and ice also produce electrical signals when they break. What was surprising was that the voltage spike sometimes preceded the avalanche by as much as 5 seconds.

"It was shocking," Shinbrot says. "We don't have any explanation for this." He and his team repeated the experiments using different types of containers and powders, including bleached and unbleached flour, plaster, and mortar. But they kept coming up with the same results. "Somehow, pulling powders apart seems to produce a voltage. There has to be something happening on the microscopic level that produces these voltages."

Scott Waitukaitis, a doctoral candidate who studies electrification in granular systems at the University of Chicago, says he suspects that the spark is created when electrically charged particles are pulled apart. Waitukaitis was impressed by how reliably the signal precedes the avalanche. "If we can predict when an avalanche will occur, we may be able to get a little bit of warning before an event like an earthquake. I think that's really big." Although a 5 second heads-up is clearly not enough time to evacuate people from an earthquake zone, Waitukaitis says that with smart grid technologies, perhaps it would be enough warning to turn off sensitive technologies that might explode or cause fires during the quake.

And because ceramic turbines and concrete bridges are also composed of fine particles, a voltage spike might also precede cracking in these structures. Shinbrot says that years or decades from now, a better understanding of the particles' electrical interactions may one day enable technologies that predict breakages before they cause catastrophic damage.

For now, Shinbrot has many more questions: Is there a voltage precursor when using larger particles such as sand or sugar? What happens when the particle sizes are mixed, like they are in the Earth's crust? And does the phenomenon differ across larger scales?

"This is a new effect, and it's very strange," Shinbrot says. "So the big question is: What on earth is going on? Either we've made a mistake, or there's something fundamental and new going on."

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